Does your AC blow cold air?Do you have the AC turned on? Or Climate set to Auto?
The is the AC clutch engaging and disengaging
The AC will cycle on and off more often specially when it is colder out.
If the AC is on the compressor runs the same whether it's set for AUTO or is run in Manual mode. All temperature control is by running some or all of the air thru the heater core after it's gone thru the AC evap section. The intent of the system is to run the evap at about 35 to 39 degrees to remove as much humidity from the air as possible. Then the dehumidified air is directed thru the heather core as needed to warm it up to the desired temperature. The cooler the air is hitting the evap the more often the compressor will cycle.Does your AC blow cold air?
I'm in no way a refrigeration expert but here's my take on what could be going on right or wrong.
If you have the Climate control set to Auto that HVAC system continuously tries to keep the temp solid per the user's temp setting.
Which could mean a lot of AC cycling on and off.
If so try turning Climate control Auto off then set the temp real low and see what happens.
On the other hand if you don't use Auto climate control and this really concerns you, i'd have the AC checked out as it could be low on freon, a pressure switch gone bad, etc.
Another thing to keep in mind is when the defroster is turned on it uses the AC to blow drier air on the windshield.
Whether that causes a lot of AC cycling maybe in cooler weather, don't know off hand.
Personally i wouldn't worry about this unless or until the AC stops blowing cold air.
Myself i never use Auto Climate for this exact reason as i think it tends to over work anything to do with HVAC system.
Jim thanks for that explanation.If the AC is on the compressor runs the same whether it's set for AUTO or is run in Manual mode. All temperature control is by running some or all of the air thru the heater core after it's gone thru the AC evap section. The intent of the system is to run the evap at about 35 to 39 degrees to remove as much humidity from the air as possible. Then the dehumidified air is directed thru the heather core as needed to warm it up to the desired temperature. The cooler the air is hitting the evap the more often the compressor will cycle.
Yes, you have it for the basics. You raise questions having to do with finer points of the design. Here's some of the finer points... Some vehicles run water thru the heater core all the time, in which case the basics are all of it. Some vehicles have a water shut off valve for the situation you highlighted "what about when it really hot?". The shutoff valve typically is set to "off" for one of these two cases.... In some systems it's off anytime the temperature control is set to full cold regardless of whether inside (recirc) or outside air is being used. In other systems it's only set to off when the system is in recirc mode. Of course some systems don't have those labels on the controls, esp AUTO systems, so it can be a bit of a crap shoot to say for sure unless you really know the system's design. I don't know if the JGC even has a water shut off valve. Here's one reason why some don't have the valve... in some cooling system designs there are separate circuits for the heads and the block and those circuits also feed the heater core in series. So if you shut off the heater core there would be no flow at all thru the heads. What they did to get around that and have a valve was to have a shunt valve, instead of an inlet and an outlet it has two inlets and two outlets, it's able to shunt the water thru the body of the valve and keep it flowing, just not thru the heater core, or it can close the shunt part and run it thru the heater core. Another reason they didn't use valves was that back "in the day" a lot of cheapskates just ran water in the radiator. The design of some AC/heater systems was such that people could run the AC and adjust the temperature up a bit so quite a bit of air ran thru the heater core to get reheated... surprisingly they found there were times the AC evap air was cold enough, probably when the car was first started and on a cool day, that it actually froze the water in the heater core and ruptured it. Supposedly this happened to Chrysler products more than others, or so I was told years ago. Many of my Chevy's had a vacuum switch in the AC control head that was activated when the temp lever was pushed to full cold and it sent vacuum to the heater core shutoff valve. I can tell you from experience that even when no air goes thru the heater core it still heats the hell out of the whole "ac/heater box" and still causes the air temp to increase at least 4 degrees over what it is if you keep the water shut off.Jim thanks for that explanation.
Yeah as i admitted earlier i'm no refrigeration expert but your explanation makes sense.
I was thinking it worked similar to a home central AC system where the AC is blowing through the furnace heat core with the furnace heat off. In that case the house temp is controlled by turning the AC on or off dependent on the thermostat set point.
So what you're saying is that the heater core always has coolant running through it when the AC is on no matter if Auto temp is on or off?
And the evap is kept at a constant temp with the cabin temp controlled by evap and heater blend vanes even when Auto is set to off?
How does this all work though in extremely hot weather when the AC cabin temp is set low as possible and where the cabin temp never meets the cabin temp set point?
Does the heater core still have coolant running through it to keep the evap from possibly icing up or does the compressor cycle off or both of the above in that condition?
Now i'm wondering how old school auto AC systems work or if they use the same principal.